Glow Plug System: Description and Operation

DESCRIPTION
Two glow plug control system are used on the 6.2L/V8-379 diesel engine, one system for heavy duty emissions (LL4 designation) and one for light duty emissions (LH6 designation). The 6.5L/V8-397 engine utilizes the same glow plug system used on heavy duty 6.2L/V8-379 engines.
The system used for heavy duty emission versions consists of an integral electronic control/glow plug relay assembly, 6 volt glow plugs, a glow plug inhibit temperature switch and a Wait lamp.
The system used for light duty emission versions, incorporates the same glow plugs, glow plug controller and Wait lamp. However, there is no temperature inhibit switch. Instead, the glow plug cycle is controlled by the ECM computer which receives temperature information from the coolant temperature sensor, located in the water crossover on the engine. The computer transmits a voltage signal to the cold advance relay in the ignition circuit to the glow plug controller. The relay is located at the junction block in the engine compartment on the righthand side of the cowl.

SYSTEM OPERATION
Normal system function operation is as follows:
1. Key-On/Engine Not Running and at room temperature:
a. The glow plugs energize (turn On), for approximately 4-6 seconds, then de-energize for approximately 4.5 seconds.
b. The glow plugs cycle On for approximately 1.5 seconds, Off for approximately 4.5 seconds and continue to cycle 1.5 seconds On/4.5 seconds Off for a total duration (including the initial 4-6 seconds), of approximately 20 seconds.
2. If the engine is cranked during or after the above sequence, the glow plugs will cycle On/Off for a total duration of 25 seconds after the engine control switch is returned from the crank position, whether the engine starts or not. The engine does not have to be operating to terminate the glow plug cycling. The times indicated here are approximate because they vary with initial engine temperature. The initial On time and cycling On/Off times vary also with system voltage and/or temperature. Lower temperatures will cause a longer duration of cycling.